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AN EXPERIMENTAL STUDY OF VISUAL 

MOVEMENT AND THE PHI 

PHENOMENON 



BY 

FORREST LEE DIMMICK 



Thesis presented to the Faculty of the Graduate School of 

Cornell University in partial fulfillment of the requirements 

for the degree of doctor of philosophy 



Reprinted from The American Journal op Psychology 
October 1920, Vol. XXXI, pp. 317-332 



AN EXPERIMENTAL STUDY OF VISUAL 

MOVEMENT AND THE PHI 

PHENOMENON 



BY 

FORREST LEE DIMMICK 



Thesis presented to the Faculty of the Graduate School of 

Cornell University in partial fulfillment of the requirements 

for the degree of doctor of philosophy 



Reprinted from The American Journal op Psychology 
October 1920, Vol. XXXI, pp. 317-332 



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6 



; MAR 261981 

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AN EXPERIMENTAL STUDY OF VISUAL MOVE- 
MENT AND THE PHI PHENOMENON 1 



By F. L. Dimmick 



TABLE OF CONTENTS 

I. Introduction 317 

II. Experimental Procedure 318 

III. Results 320 

General 320 

Pure Phi Phenomenon 330 

Object-Stimuli 330 

Colored Stimuli 330 

Korte's Reverse Movement 331 

Nature of the Process-Configurations 331 

IV. Conclusion 332 

Introduction 

In his " Experimentelle Studien iiber das Sehen von Be- 
wegung " 2 Wertheimer reports the isolation of a new ele- 
mentary mental experience, that of movement. To keep it 
distinct from the perceptual complex in which it usually oc- 
curs, he calls it Phi or the Phi phenomenon. Analysis of it 
reveals nothing for him but just the movement-experience; 
it has no visual quality ; it has only spatial localization and 
direction. 

The aim of our investigation is to put this elementary move- 
ment-experience, this Phi phenomenon, under critically de- 
scriptive conditions, and to test its analysability. 

The term ' movement sensation ' has been in common usage for a 
long time. Exner 3 first gave to it the meaning, in a pregnant sense, 

1 From the Psychological Laboratory of Cornell University. 

2 M. Wertheimer, Ueber das Sehen von Bewegung, Zeit. f. Psych, 
u. Phys. d. Sinnes., 1 Abt. 61, 1912, 161. 

3 S. Exner, Ueber das Sehen von Bewegungen, Wiener Sits. Ber., 
Abt. 3, 72, 1875, 156. 

317 



318 DIMMICK 

of a primary and elemental experience. He cites experiments to 
demonstrate its immediacy, and points out its fulfillment of the char- 
acteristics of sensation. The peculiar nature of the movement experi- 
ence was again emphasized by Schumann, 4 and an experiment to 
demonstrate its simplicity was indicated. Wertheimer followed closely 
the cue given by Schumann. He chose the simplest conditions under 
which the impression of movement could be obtained. Two lines, 
differing in position, were presented successively in the Schumann 
tachistoscope. The principal stimuli were a pair of parallel horizontal 
lines, and a pair of lines set at an angle to each other. A number of 
variations of these two stimuli were made in order to test the effect 
of different conditions. The O's seem not to have been given specific 
instructions, but to have been allowed to report spontaneously what 
they experienced. They were, of course, kept in ignorance of the 
nature of the stimulus. Only three O's were considered necessary, 
both because those with whom the work was started agreed well with 
one another, and because the reports were immediate. 

The important determinant for movement, with the above stimuli, 
Wertheimer finds to be the temporal interval elapsing between the 
presentations of the two members. There is an optimal time, 60 , at 
which the movement of a line all the way from the one position to the 
other results. With intervals either larger or smaller, the movement 
experienced is not complete. As a rule two objects are seen, both 
moving more or less, but not moving over the entire field. Such an 
experience we shall call bimembral movement. It sometimes happens 
that only one of the members seems to move, while the other remains 
stationary. This experience may be designated unimembral movement. 
A fourth type of movement is that in which there is no change of 
position of either member, but only a movement within a member 
itself, an intramembral movement. Under occasional or demonstra- 
tional conditions, Wertheimer is able to get the movement-experience 
alone, independent of any substantive perception and with no visual 
quality. Because it can thus exist in its own right, it is given the 
designation Phi or the Phi-phenomenon. It is this Phi, then, which, 
when added to the perception of a line in two successive positions, 
gives the impression of movement. It is the basis, too, of that seen 
movement which is correlated with a physically moving stimulus. 
The observations which he made led Wertheimer to outline a physio- 
logical theory of a short-circuit of nervous excitation in the cortex 5 as 
the basis of the Phi-phenomenon. 

Experimental Procedure 

For our experimental work, we used a modification of the 
Dodge tachistoscope which enabled us to present successively 
the two members of a bimembral stimulus. In addition it 
gave us control over the pre- and post-exposure fields. 

The particular modification which we made of the Dodge instrument 
was the addition of a third stimulus-field by insertion of a second 
transparent mirror. A group of three plain-glass nitrogen-filled lamps 
(two 200 watt, and one 100 watt) furnished illumination for the stim- 
ulus-fields. They were placed at the ends of a set of three parallel 
tubes of about 5 cm. diameter. The light conducted down the tubes 

4 F. Schumann, Ber. u. d. II Kong. f. exp. Psychol., 1907, 218. 

5 Op. cit., 248. 



STUDY OF VISUAL MOVEMENT AND PHI PHENOMENON 319 

was reflected from mirrors to the respective stimulus-fields. Between 
the lamps and the open ends of the tubes was placed a falling shutter, 
so designed that the exposures of the three fields were independently 
variable. The openings through which the light entered the tubes were 
horizontal slits, 1 cm. by 4 cm. To give additional control, an auxiliary 
shutter was set in every tube a little way from its open end, and with 
it a diaphragm which made possible the equation in sensible brightness 
of all three fields. The shutter fell from a constant height by its own 
weight when the current was broken through an electromagnet. The 
friction, as the falling shutter ran in the guides, was slight and the 
variation in time of fall proved negligible. 

This arrangement made it possible for us to start with any pre- 
exposure field, to present the first member of the stimulus for a given 
length of time, then after a variable interval (during which the pre- 
exposure field was repeated) to present the second member for the 
desired length of time, and then to return to the pre-exposure field. 
The shutter permitted of total times up to 380; 210 o- was the longest 
needed. The eye-piece of the exposure apparatus was inside a dark 
chamber, and the O was allowed 10 min. to become partially dark- 
adapted before work was begun. 

All of the stimuli described by Wertheimer were repeated, 
and six object-pictures of our own were added. The greater 
part of our work was done with two arrangements, the one 
of which gave movement from an oblique to a horizontal posi- 
tion, and the other from an upper horizontal to a lower 
horizontal position. There were four pre-exposure fields : 
A, uniform white, identical with the background of the stimu- 
lus-cards ; B, similar to A, with a black fixation-point at the 
middle of the field ; C, uniform lightless field ; D, unlighted 
field, bounded at the top and bottom by luminous lines. 

The exposure-time for each member of the stimulus was 
kept constant at 30o\ The time-intervals were 30<rcr09 ' 90 a,, 
120 a-, 1 50 a. They cover the range given by Wertheimer from 
near simultaneity to the region of succession. The principal 
stimuli, the angle and the horizontals, were presented in series 
of five exposures with every pre-exposure field, at every time, 
and to every O. Four other stimuli were presented to every 
O in the same sort of series, but with only two of the pre- 
exposure fields ; they were so chosen that every stimulus was 
studied by one or two O's and with two to four pre-exposure 
fields. A haphazard order of fields, times, and stimuli was 
followed in the presentation of the series. 

Two different sets of instructions were given to the O's, 
thus duplicating the above set of series. The one of these, 
which we shall call the ' process ' instruction, was : " A stimu- 
lus will be shown you which will arouse a visual perception. 
Describe this perception in strictly psychological terms as ac- 
curately as you can. Report no process of which you are not 
sure. The stimulus will be repeated to complete the descrip- 



320 DIMMICK 

tion." The other set, the ' meaning ' instruction, ran : " A 
stimulus will be shown you which will arouse a visual per- 
ception. Characterize this perception as fully as you can. 
The stimulus will be repeated to complete the characteriza- 
tion." To three O's the process-instructions were given first, 
and the entire group of series was repeated with the meaning- 
instructions. Three other O's were required to give meaning- 
reports first, and were then shifted to the process-attitude. 
The two most practised O's were instructed in successive 
series either for process or for meaning by chance, and every 
series was repeated later with the alternate instructions. Ex- 
cept for the last two, the O's were required to read the in- 
structions at the beginning of every observation hour. Before 
the regular work was begun, trial series were taken until the 
reports gave evidence of adequacy and stability. 

The eight O's who served were: Miss C. Comstock (C), 
graduate student in psychology; F. L. Dimmick (D), assistant 
in psychology; Dr. L. B. Hoisington (H), instructor in psy- 
chology; Miss M. F. Martin (M), graduate scholar in psy- 
chology; Miss A. H. Sullivan (S), graduate fellow in psychol- 
ogy; S. A. Takaki (Ta), graduate student in psychology; 
S. A. Tung (Tu), graduate student in psychology; and Mrs. 
A. K. Whitchurch (W), graduate student in psychology. 
Observers C, D, H, and S were practised; M, Ta, Tu, and 
W were relatively unpractised. 

O sat with his head in the (hood of the instrument. The 
auxiliary shutter was opened, a ready-signal given, the ex- 
posure shutter dropped, and the auxiliary shutter closed. 6 O 
then gave his report according to the instructions. The ex- 
posure shutter was raised to the starting position, and the 
stimulation and report repeated, until the series of five was 
completed. A rest of 2 or 3 minutes was permitted while 
the apparatus was reset for a new series. The above pro- 
cedure was followed for the 160 series with every O. 

Results 
Table I summarizes quantitatively the results obtained with 
the two principal stimuli. Under our conditions, all O's per- 
ceived optimal movement of the horizontal lines in more than 
50% of the cases, and only one fell below that percentage 
with the oblique-to-horizontal movement. Of the perceptions 

6 The function of the auxiliary shutter was to shut off all light from 
passing down the tubes save when a true exposure was made. It 
eliminated the possibility of a false exposure when the falling shutter 
was raised to its starting position. 



STUDY OF VISUAL MOVEMENT AND PHI PHENOMENON 321 

of partial movement, unimembral movement shows itself much 
more frequently than bimembral for all but two O's. Simul- 
taneity and succession occur but rarely. Closely paralleling 
the above perceptions are the percentages of reports, under 
the instructions to ' describe in psychological terms,' in which 
some visual process was present in the field between the two 
members of the stimulus. The number of times when the 
entire spatial interval was involved agrees with the number 
of optimal movements perceived; the frequency of cases in 
which the process in the interval accrues to one of the mem- 
bers and not to the other is approximately the same as that of 
the reports of unimembral movement ; processes which involve 
both members but not the entire field occur as often as does 
bimembral movement. 



TABLE I 

Process Configurations and Movement Perceptions 
(Percent, of 100 Reports for Every O) 

Horizontal Lines Oblique Line and Horizontal 



Obs. 


Total 


Uni- 


Bi- 


None 


Total 


Uni- 


B 


L- 


None 




P 


M 


P 


M 


P 


M 


P 


M 


P 


M 


P 


M 


P 


M 


P M 


C 


78 


77 


20 


15 


3 


8 








48 


35 


43 


58 


8 


6 


1 1 


D 


66 


61 


22 


21 


12 


16 





2 


77 


73 


12 


14 


11 


14 





H 


66 


56 


24 


24 


3 


15 


7 


5 


67 


66 


25 


19 


5 


10 


3 5 


M 


72 


65 


23 


21 


1 


11 


4 


3 


100 


88 





12 











S 


77 


69 


6 


7 


13 


23 


4 


1 


90 


72 


1 


23 


1 


7 


8 


Ta 


63 


52 


25 


28 


10 


17 


2 


3 


60 


65 


30 


33 


7 


2 


3 


Tu 


77 


69 


22 


21 


2 


9 





1 


80 


69 


20 


29 





1 


1 


W 


60 


53 


21 


22 


19 


25 








68 


77 


19 


15 


13 


8 





Average 


70 


63 


20 


20 


8 


15 


2 


2 


74 


68 


19 


25 


6 


6 


2 1 


Mean Var 


. 6 


7 


4 


4 


6 


5 


2 


1 


13 


10 


11 


11 


4 


4 


2 1 



Uni-, Bi-,= experiences of unimembral and of bimembral movement. 
P= Process configuration; M = meaning characterization. 



TABLE II 

Optimal Movement with Different Backgrounds 
(Percent, of 25 Reports for Every O) 

Horizontal Lines Oblique Line and Horizontal 



Obs. 


A 


B 


C 


D 




\ 


; 


B 


C 


D 




P 


M 


P 


M 


P 


M 


P 


M 


P 


M 


P 


M 


P 


M 


P 


M 


C 


100 


76 


53 


76 


73 


80 


87 


76 


53 


56 


59 


52 


40 


24 


40 


8 


D 


60 


40 


76 


48 


72 


60 


60 


96 


64 


68 


68 


64 


80 


88 


96 


72 


H 


56 


56 


72 


80 


72 


68 


64 


52 


72 


48 


72 


92 


64 


68 


60 


56 


M 


76 


67 


56 


53 


68 


67 


88 


73 


100 


100 


100 


100 


100 


40 


100 


52 


S 


84 


87 


72 


93 


72 


40 


88 


53 


96 


60 


92 


60 


80 


93 


92 


73 


Ta 


67 


40 


53 


48 


53 


56 


80 


64 


67 


60 


60 


76 


67 


60 


47 


64 


Tu 


73 


68 


93 


68 


67 


68 


73 


72 


80 


68 


87 


84 


73 


52 


80 


72 


W 


68 


60 


60 


53 


52 


53 


60 


47 


64 


80 


60 


67 


76 


67 


72 


93 


Average 


73 


62 


67 


65 


66 


62 


75 


67 


78 


68 


75 


74 


73 


62 


73 


62 


M. V. 


10 


11 


11 


13 


7 


8 


11 


13 


15 


12 


14 


14 


11 


17 


19 


17 



32; 


> 




DIMMICK 
















TABLE III 














Optimal Movement with Different Temporal Intervals 












(Percent, of 20 Reports for Every 0) 












Horizontal Line^ 




Oblique 


Line and Horizontal 


Obs 


. 30 
P M 


60 


90 120 150 


30 60 


90 


120 


150 




P M 


P M P M P M 


P 


M P M 


P M 


P 


M 


P M 


C 


67 55 


92 95 


92 90 83 80 58 65 


25 


62 50 


75 70 


50 


35 


25 20 


D 


50 75 


90 65 


80 85 80 45 30 35 


70 


45 95 90 


95 95 


70 


70 


45 65 


H 


55 50 


80 65 


80 75 65 60 50 30 


50 


65 90 95 


90 90 


55 


75 


50 30 


M 


50 75 


75 92 


90 75 75 75 70 8 


100 


83 100 100 


100 100 


100 


100 


100 58 


S 


60 83 


90 92 


95 92 95 42 45 33 


100 


92 85 100 


95 92 


100 


42 


70 33 


Ta 


50 70 


83 55 


92 65 42 35 50 35 


50 


50 83 60 


92 100 


50 


75 


25 40 


Tu 


75 70 


100 95 


100 85 50 55 58 40 


75 


75 83 90 


100 80 


90 


60 


50 40 


W 


15 25 


70 75 


90 83 75 42 50 42 


60 


67 70 92 


100 100 


80 


67 


30 58 


Av. 


53 64 


85 79 


90 81 71 54 51 36 


66 


72 84 85 


93 91 


74 


66 


49 43 


M.V.12 14 


7 14 


5 7 14 13 8 10 


20 


21 9 15 


6 8 


18 


15 


18 13 



In Tables II and III the results have been arranged to 
indicate the influence of the pre- and intra-exposure field and 
of the temporal interval between members. Individual varia- 
tions appear with the various fields, but they show no uniform 
tendency, and their nature is indicated in some cases in the 
introspections. C often objected that the fixation-point on 
pre-exposure field B interfered with her reports of process ; 
S complained of the dark backgrounds. It is significant, how- 
ever, that the process-reports and the perceptive characteriza- 
tions parallel each other. This agreement is very evident 
when the averages for the group are taken, and it is further 
supported by the fact that the mean variations are not ex- 
cessive. We may conclude, then, that the kind of pre-expos- 
ure field employed had no general and constant effect on the 
perception or its process-configuration. 

Table III, on the other hand, brings out a very definite in- 
fluence of the temporal interval. The O's vary among them- 
selves, but they agree in that they have curves of percentages 
which are high for the middle values of the temporal interval 
and low for the extreme values. Process-reports and per- 
ceptive characterizations run parallel. The averages, of course, 
show the conformity even more prettily. Time-interval 90cr 
has the highest average percent, of optimal movement and of 
total configurations; 30crand 1 50 cr have the lowest. Just as 
significant is the fact that the mean variations are smallest 
at the middle value. The larger variations among O's occur 
with the longer or shorter times. 

The evidence of the values, in the above tables, of the various 
perceptive characterizations indicates unquestionably that we 
have reproduced the essential factors of Wertheimer's condi- 
tions. Table I shows that our temporal intervals lie between 
those which give succession and simultaneity. The two forms 
of partial movement appear frequently, but optimal movement 



STUDY OF VISUAL MOVEMENT AND PHI PHENOMENON 323 

predominates. The ineffectiveness of variations of the pre- 
exposure field does not contradict Wertheimer's observation 
that the color of the stimulus did not affect the perception. 
Finally, the behavior of the perception with the different time- 
intervals is exactly that which Wertheimer suggests, though 
he makes no precise statement. 

On the other hand, in the column in which Wertheimer 
would write ' nothing,' under the heading ' process,' we have 
found a closely parallel set of values which represent the con- 
figurations of visual process present in the movement-field 
when the O's were set to describe the experience. The nature 
of the visual experience which filled the interval can be pointed 
out most clearly by direct reference to the introspections. 

Optimal Movement; Meaning Reports; Stimulus I 

C. A horizontal line appeared in the upper part of the field, moved 
down to a lower position, and stopped ; the movement was slow, 
smooth, and continuous. 

D. I saw a horizontal line move quickly from a position above the 
fixation point to one below, and disappear. It seemed to come in, 
move down, and go out, as if that were only a part of some larger 
movement. The movement was rapid but smooth. 

H. A black horizontal line appeared and moved down very rapidly, 
and then came to rest in a lower position for a short time. The move- 
ment was uniform but very fast. 

M. A line moved from an upper horizontal position to a lower one ; 
it slowed up just before it reached the final position; the movement 
was continuous all the way from one to the other. 
S. A rectangle moved down smoothly and stopped for an instant. 
The speed of the line increased as it moved, and was very rapid just 
before it stopped. 

Ta. A horizontal line appeared in the center of the field and moved 
down smoothly ; it became shorter as it moved, and stopped in a 
position lower down. 

Tu. A line dropped downward very smoothly and rapidly, until it 
reached the lower position, and then disappeared. 

W. I saw a line drop smoothly and quickly from one position to 
another. 

Stimulus II 

C. I saw an oblique line which moved down across the field to the 
horizontal with a smooth and continuous movement. 

D. A dark grey rectangle moved smoothly and rapidly from an 
oblique position to a horizontal. 

H. An oblique line fell down into a horizontal position. The move- 
ment was continuous, but faster just before it reached the final position. 
M. An oblique line moved down through an arc to the horizontal. 
S. An object in the oblique position fell to the horizontal. The 
movement was rapid, and stopped short at the end. 
Ta. An oblique line appeared, turned downward, and took the hori- 
zontal position. The movement was smooth. 

Tu. I saw an oblique line first, and it moved steadily down into a 
horizontal position. 

W. The oblique fell rapidly into the horizontal; I saw movement all 
the way. 



324 DIMM1CK 

Process Reports; Stimulus I 

C. At the upper part was a black horizontal extent which immediately 
gave place to a grey patch below and joining it. The bottom of the 
grey was darker and at that place appeared later a black extent similar 
to the first. The grey changed in quality ; it was one continuous ex- 
tent, but it was different at different places. 

D. A black line appeared just above the middle of the field. It dis- 
appeared, and extending down from where it had been was a grey 
band, light at the top and dark at the bottom, and at the lower side 
was a very dark strip of grey. The grey patch did not change in 
extent, but the patterning of brightnesses changed. 

H. The upper line was not definite at the lower edge, but fused into 
a filmy grey that was a little darker at the right and left extremes, 
and terminated in a black process lower down. 

M. There was a line of very dark grey at the top, and immediately 
below a darkening of the field in the general form of a rhombus, the 
edges of which were fuzzy but fairly definite. At the bottom of this 
figure was a definite line, and in the middle a darker streak which 
could hardly be called a line. 

S. At the top was a black rectangle, clear and intense. Below was a 
grey patch, longer in the horizontal dimension, but not clear. At the 
bottom was a definite line. 

Ta. At first an irregular rectangle, black and sharp at the top, ap- 
peared. Its lower side was grey and blurred. Below was a wide grey 
line, sharp at the bottom but indefinite above. The lower and upper 
sides of the upper and lower lines respectively shaded off and joined 
each other. 

Tu. First, there was a line above the middle of the field ; below it, a 
dark grey which faded out farther down until it reached a lower 
horizontal line, the upper part of which was grey and indefinite, the 
lower part black and sharp. 

W. A horizontal line appeared and disappeared, and below where it 
had been there was a wide grey rectangle of light tint at the top, 
medium in the middle, and dark at the bottom. Below appeared a 
second line. 

Stimulus II 

C. First there was a black oblique at the top, which immediately 
became greyer, and then was replaced by a grey patch, which extended 
down to the horizontal, where a line appeared. 

D. The oblique came in first; then below it there was a grey which 
extended down to a horizontal line below ; this grey was not uniform 
but light and dark in streaks. 

H. An oblique line appeared and then a horizontal, and between them 
the field was grey in a solid fan-shape. 

M. An oblique appeared ; then below it there came a sector of pale 
grey which was darker near the bottom, where it became a more defi- 
nite line. The first line had faded out before the last one came. 
S. A black oblique line appeared ; then something grey came below 
it which was rather indefinite, and extended down to the horizontal 
line. 

Ta. I saw an oblique line which was blurred downward. The upper 
part was black and clear-cut. The lower part shaded off into a grey, 
at the bottom of which came a horizontal line. 

Tu. I saw an oblique line and a horizontal, and the space between 
them was grey. The oblique was wide and had no definite outline on 
the lower side. 



STUDY OF VISUAL MOVEMENT AND PHI PHENOMENON 325 

W. An oblique line appeared and disappeared, and then a horizontal 
came below. Between the two was a triangular light grey patch, which 
was darker near the bottom line. 

Unimembral Movement; Meaning Reports; Stimulus I 

C. A horizontal line moved down smoothly but not continuously. 
It moved part-way, then disappeared, then reappeared lower down and 
stationary. 

D. The first line appeared and remained stationary. Below it another 
line came in, moving downward. The movement was over most of 
the space between the two positions, but was of the lower line. 

H. A line appeared in the upper part of the field for an instant ; 

then a little lower down something moved into the field, and stopped 

as a black line at the bottom. 

M. A horizontal line came into the part of the field moving, then 

another appeared lower down and stationary. 

S. A line moved down smoothly, getting faster as it went, and then 

the end-position stood out, sharp and stationary. 

Ta. A line moved down, and as it moved another appeared lower 

down and remained stationary. 

Tu. First I saw a line which wavered but did not change position, 

and at the same time there was something moving down into a position 

below. 

W. A line dropped into a lower position. The motion was best near 

the bottom, and there was a blank space just below the top position. 

Stimulus II 

C. An oblique and horizontal appeared, and the first moved down 
toward the second but never reached it. 

D. I saw two lines, one oblique and one horizontal. The latter re- 
mained stationary, and the oblique moved down toward it, but was 
gone before reaching it. 

H. An oblique line came in and moved downward, and below it stood 
a horizontal line. 

M. An oblique line moved down toward the horizontal. The move- 
ment was jerky and definitely of the oblique, not of the horizontal. 
S. I saw a line move down very rapidly through an arc. The first 
part of the movement was not clear, i.e., it seemed to be part way 
down before I saw it ; above was a blank. 

Ta. An oblique line appeared, then a horizontal, and the oblique 
moved down to the horizontal. 

Tu. An oblique line appeared in the upper part of the field and moved 
down faster and faster Until I could not see the movement. Then the 
horizontal came in. 

W. An oblique line moved rapidly to the horizontal. The movement 
was best at the beginning, and just at the bottom there was a space 
of no movement at all. 

Process Reports ; Stimulus I 

C. I saw a black line ; and below it was a grey band which was not 
uniform in quality, but which had no definite lines in it. Below was a 
second sharp black line. 

D. Two lines came successively. The upper was clear-cut and sta- 
tionary; the lower was at first a band of greys, the upper edge of 
which was indefinite and concave. 



326 DIMMICK 

H. A black line appeared in the upper part of the field. Below and 

detached from it by a bright streak was a rather indefinite grey, which 

fused into a black line lower in the field. 

M. First came a line in the upper part, then a grey, and another line 

below. The grey joined the lower line but was separated from the 

upper by a bright streak. 

S. I saw a horizontal line, then lower down another with a grey patch 

above it. 

Ta. The first line was wide ; the upper part black, the lower part grey 

and blurred. There was a bit of white background between this and 

the lower line. 

Tu. There was a sharp definite line. Just below it was white, and 

all the rest below was grey, darkening downward until it joined the 

lower line. 

W. I saw two horizontal lines, one below and after the other. A 

band of greys extended up from the lower toward but not to the upper. 

Stimulus II 

C. There was a wide patch of grey in the shape of a sector. It was 
dark at the top and shaded off into light grey downward. The grey 
did not reach to the horizontal line which came in at the bottom. 

D. A sharply defined oblique line appeared and then a horizontal. 
When the horizontal came, the field just above it was greyish. 

H. First there was an oblique line with a patch of bright field just 
below it; then at the bottom a narrow sector of light grey, which was 
later replaced by a horizontal. 

S. A black oblique appeared first; below it was white. Then came 
a horizontal line, with an oblique grey on its upper edge. 
Ta. The oblique was grey on its lower side and blurred downward. 
There was a white space between it and the horizontal line. 
Tu. I saw an oblique line clearly ; then the background below it be- 
came dark at the top and light lower down. At the bottom there was 
a horizontal line with a white streak above it. 

W. A distinct oblique line appeared at the top, then a horizontal, and 
between them a series of grey triangles, light at the top and dark at 
the bottom and joined on to the lower line. 

BlMEMBRAL MOVEMENT; MEANING REPORTS ; STIMULUS I 

C. A horizontal line moved down and stopped. The movement was 
not continuous ; there was a place in the middle where it disappeared 
entirely. Farther down it came back again. 

D. A horizontal line appeared and started to move, then disappeared, 
but reappeared lower down, and moved into the lower position. 

H. A heavy black line appeared and started to move, but disappeared. 

Part way down it reappeared, and moved into the lower position and 

stopped. 

M. Two black horizontal lines appeared and both moved down a little. 

S. An object appeared and moved downward. A little way below 

another line appeared, and moved down and stopped. 

Ta. A line appeared, moved down and disappeared ; after a short 

space another appeared, and moved down and stopped. 

Tu. A horizontal line moved down very rapidly, disappeared for an 

instant, then moved down again into the lower position. The upper 

part of the movement was the more rapid. 

W. The line moved down quickly but with a flicker, i.e., it started 

to move, there was a break, then the last part of the movement came 

out distinctly. 



STUDY OF VISUAL MOVEMENT AND PHI PHENOMENON 327 

Stimulus II 

C. An oblique line moved down to the horizontal. The movement 
was not smooth ; it disappeared in the middle so that there was a blank 
space. 

D. An oblique appeared and began to move, but very soon disap- 
peared. Then a horizontal appeared, which seemed just at the end 
of a movement down. 

H. The oblique started moving, then for a bit I saw nothing, then 
the line moved from just above into its horizontal position. 
S. An oblique line moved down to the horizontal, but there was a 
pause in the movement part-way down. 

Ta. An oblique line came in and started to move, but soon faded out ; 
then something below jumped in, and moved down to the horizontal. 
Tu. An oblique line moved down to the horizontal but not smoothly; 
there was a flash of good movement at the beginning and end. 
W. An oblique line dropped to the horizontal, but I did not see move- 
ment all the way. There was a blank in the middle. 

Process Reports ; Stimulus I 

C. I saw a line in the field above the middle. Its edges were not 
sharp, and it shaded off at the lower side. Below appeared another 
line, which was surrounded with grey at first and then became quite 
distinct. 

D. A horizontal line came in with a grey blur on the lower side. 
The grey extended farther down from the extremities of the line than 
from the middle, so that its lower side was concave though not sharply 
outlined. The second line had a similar grey above it. A roundish 
patch of white background was left between the two. 

H. I saw a black line a little above the middle of the field, then an- 
other below the middle and equal in extent to the first. Between was 
a grey, with a slight gap of bright field in it. 

M. There appeared two lines of grey. Both were indistinct on the 
edges that were toward each other. 

S. I saw a line that was clear and black at the upper edge but indis- 
tinct below. Then came a space in which there was nothing, and then 
I saw a hazy line at the bottom. 

Ta. The first line was grey all over and a little wider at the ends ; 
the middle part had no definite outlines. The second line had black 
and clear outlines at the ends but the middle part was indefinite at 
the top, and the grey margin of it was a little concave. 
Tu. First an upper and then a lower horizontal appeared, and the 
space between was grey except at the center, where it was the same 
as the background. 

W. I saw a horizontal line, then another below it. Between them 
was a blur of grey, darker at the top and bottom and white in the 
middle. 

Stimulus II 

C. I saw an oblique line. It disappeared and the field was only white, 
then a horizontal appeared. Both lines were indistinct and blurred 
toward the interior of the angle. 

D. I saw an oblique line. It disappeared and I saw a horizontal. 
The oblique was at first a sharp line, then it shaded off into the back- 
ground below it. The horizontal was indefinite along its upper edge 
when it came. 



328 DIMMICK 

H. An oblique line appeared which was not sharply outlined. Just 
below it was a very light grey. Then a horizontal appeared, which 
was indefinite on its upper edge at first but soon became sharply out- 
lined. 

S. First there appeared an oblique line, which was not clear at the 
lower edge but shaded off into grey. Below there was an interval of 
white, and at the bottom a horizontal which also lacked definition. 
Ta. The upper side and end of the oblique had clear-cut outlines, but 
the lower side was greyish and blurred down. The upper side of the 
horizontal had no definite outline. 

For the demonstration of bimembral movement, Wertheimer 
recommends a stimulus consisting of two squares for the first 
member and a horizontal line for the second. This stimulus 
aroused bimembral movement in 94% of the times it was pre- 
sented to our O's and corresponding process-configurations in 
84% of the times it was given under the process-instructions. 
The typical reports are as follows : 

Meaning Report; Special Stimulus 

C. I saw a horizontal line and above it two squares. All three moved 
down a little and then disappeared. 

Process Report 
C. Two squares appeared in the upper part of the field. They were 
grey and indefinite at the bottom. Below them came a black horizontal 
line, which shaded off into grey at the top. 

The parallel values for the percentage of the three forms 
of movement are sufficient evidence that every perception of 
movement of these sorts has a corresponding process-config- 
uration. The conclusion is further substantiated by the fact 
that in a number of reports the O's have stated that a certain 
movement had a particular process-aspect and conversely that 
when, for instance, the grey was spread over the whole field, 
the movement was best. 

Wertheimer's fourth movement phenomenon, intra-mem- 
bral movement, appears according to his statement in the 
stage of simultaneity. Our O's, likewise, reported a number 
of cases, when the temporal interval was shortest, in which 
the lines stood still, but in which there was a quick " jerking 
back and forth " or an " unsteadiness " as if the line moved 
inside itself. Under similar conditions, with the instruction 
to report process, the lines were sometimes of a multiform 
grey, variously patterned. Further analysis of intramembral 
movement, with the stimuli which Wertheimer says are espe- 
cially favorable for its arousal, confirms what we have already 
said. Typical reports are as follows: 



STUDY OF VISUAL MOVEMENT AND PHI PHENOMENON 329 

Intramembral Movement; Meaning Reports; Stimulus III 7 

C. The line seemed to double over on itself at the middle; that is, 
there seemed to be a smooth gliding movement from left to right 
within the line which did not, however, change position. 
W. I saw a horizontal line in which there seemed to be movement 
across, left to right. It was not movement from one position to an- 
other, for there was only one line and the movement was within it. 

Stimulus IV 8 

S. There was a square which contracted and expanded as if it were 

elastic. 

Ta. A square appeared and stretched to right and left. 

Stimulus V 9 

M. An oblique line appeared and shrank towards its upper end until 
it became almost a square. 

Tu. There appeared a line in the oblique position which seemed to 
move toward its upper end, but did not change its general position. 

Process Reports ; Stimulus III 
C. I saw a horizontal line which was black at the right end, dark 
grey at the left, and light in the middle. The left-hand part was not 
evenly outlined, and there was no definite line where it joined the 
black part. 

Stimulus IV 

S. First a black square appeared ; then in its place was a greyish 
rectangle longer in the horizontal, then one darker and longer, then 
one black and slightly shorter. 

Ta. I saw a black square which was fairly clearly outlined at first. 
Then it became greyish, and to the right of it was a horizontal line of 
dark grey. Then the whole figure was a horizontal line black at the 
left end and lighter toward the right. 

Stimulus V 
M. An oblique line appeared. Then it was lighter at the lower end, 
and shaded into a dark grey upward. At the top was a sharp black 
square. 

Tu. First I saw a dark grey oblique line; its upper end was darker, 
with a light place just below it. The lower part of the figure faded 
out into a light grey. 

Movement within an object without change of position 
of that object thus presents nothing new. Under the char- 
acterization-attitude, it is movement on a par with the change 
of position of a form or object; descriptively, it is reflected in 
consciousness as the visual quality grey. 

7 Stimulus III consisted of two horizontal lines, the second of which 
was in a line with but to the left of the first. 

8 Stimulus IV consisted of a square and a horizontal line of the 
same width. The centers of the two forms came at the same point. 

9 Stimulus V consisted of an oblique line and a square of the same 
width. The square came at the upper end of the position of the line. 



330 DIMMICK 

The Pure Phi Phenomenon 
Finally, a number of cases of Wertheimer's pure Phi were 
reported by our O's. Frequently the line was not seen during 
the movement; there was simply " something moving " or just 
" movement." Sometimes neither of the lines was clearly per- 
ceived ; just a bit of movement downward. The cases in 
which both lines were perceived with only movement between 
are entered in Table I as optimal movement, and are paralleled 
by total process-configurations. The appearance of movement 
detached from its object occurred, as Wertheimer notes, when 
the stimulus was new or for some other reason was incom- 
pletely perceived. Under exactly these same conditions, but 
with the instructions to report process, our O's noted a flash 
of grey without the usual limiting lines above and below. 

Object-Stimuli 
The remaining stimuli which were given by Wertheimer 
and which we repeated yield results agreeing with those al- 
ready reported, but add nothing new to our analysis of the 
perception of movement. The six object-pictures which we 
added to Wertheimer's list showed the effect of central asso- 
ciations by giving optimal movement over the whole range of 
our conditions, and total configurations of process in all but a 
very few cases. 

Colored Stimuli 

In the description of the stimuli used in his experiments, 
Wertheimer tells us that he varied the color of the members. 
In another place he remarks that partial movement results 
when the two members are not of the same color. Aside from 
this, the implication is that one color gives movement as well 
as another. After our main series had been completed, we 
presented stimuli of various colors to our O's. The stimuli 
were shown in series of ten exposures at the optimal time 
(90 cr) and with a pre-exposure field of the same quality as 
the background. The colors of these stimuli were red, green, 
and blue on white backgrounds, white and yellow on black 
backgrounds, red on a green background, and blue on a yellow 
background. 

Movement, optimal in all but a few cases, was reported by 
all O's for all colors and backgrounds when the instructions 
were to ' characterize.' Under the descriptive attitude there 
was always noted a grey patch covering the space between the 
two members. When the backgrounds were white or a light 
color, the grey was a little darker than medium. On the black 
field it appeared whitish. We may state, then, with assurance 



STUDY OF VISUAL MOVEMENT AND PHI PHENOMENON 331 

that the grey which is the psychological equivalent of the per- 
ceived movement is under our conditions independent, for its 
quality, of the quality of the members of the stimulus, but 
shows an influence of the background which has the appear- 
ance of a brightness-contrast effect. 

Korte's Reverse Movement 

Korte, 10 in a later investigation, studied the perception of movement 
backward from the second member to the first, which, he said, resulted 
from making the second member more " intense " and by directing the 
attention to it. He varied " intensity " either by making the second 
member wider than the first, or by putting short perpendiculars across 
its ends. With an increase in " intensity " merely, only a slight back- 
ward jerk appeared. Neither was attention to the second line suffi- 
cient alone; but with an increase of "intensity" and a direction of 
the attention to the second member, the backward movement was 
plainly evident. 

We attempted to repeat Korte's conditions. Our stimuli with mem- 
bers of different " intensities " were a grey line on white followed by 
a black line of the same width; a grey line on black followed by a 
white line of the same width; a black line of 1 mm. width on a white 
background followed by a black line of 4 mm. width ; and a white line 
on black followed by a line of the same size with short perpendiculars 
across the ends. At first the O's were given the usual meaning- 
instructions, and a series of ten exposures was presented. Then they 
were instructed to attend to the more " intense " line, and ten more 
exposures were made ; and finally they were asked to try to get the 
line to move from the more " intense " position to the other. The 
perception was always from the member presented first to the second, 
save for a very few instances with the third instruction when O re- 
ported that perhaps there might be a hint of a jerk backwards; but 
even then no positive movement, such as they had seen with the other 
stimuli, was perceived. 

We have repeated Korte's conditions as nearly as his description of 
them permits ; and to his stimuli, which give spatial and form insist- 
ence, we have added intensive insistence. Since we never get a posi- 
tive movement-perception as we do under Wertheimer's conditions, it 
seems evident that we are not in the presence of compulsory condi- 
tions, and that the two perceptions are not of the same order. 11 

The Nature of the Process-Configuration 

Now that we have pointed out the quality of the psycho- 
logical correlate of Wertheimer's Phi, we must emphasize that 
this is but one of its attributive aspects. It must not for a 
moment be assumed that it is a simple text-book grey, the grey 
that lies at the center of the color-pyramid, or the grey of a 
piece of grey paper. The temporal attribute is beaten up with 

10 A. Korte, Kinematoskopische Untersuchungen, Zeit. f. Psych, u. 
Physiol, d. Shines., 72, 1915, 193. 

11 We are engaged in further experiments of this kind, the results 
of which will be reported later. We are also repeating certain ex- 
periments of F. Kenkel and V. Benussi. 



332 DIMMICK 

the quality into an integration of the first order. All O's 
describe the experience as a " flashing/' " flickering," " un- 
steady," "shimmery," " flame -like," "liquid," "live" grey. 
It is further reported as a " curtain " or " film " which is not 
superficial but hardly bulky. The background seems at times 
to shine through the interstices of the grey, giving it a sort 
of transparency. In texture it resembles the Fldchenfarbe 
described by Katz 12 and the adaptation-film of Sheppard. 



13 



Conclusions 

We have, in this investigation, been concerned primarily 
with a critically descriptive analysis of the reflection in con- 
sciousness of a stimulus-complex which is compulsory for the 
visual perception of movement. We have found that this 
reflection in consciousness takes the form of a primary in- 
tegration of a visual quality (grey) with a duration which is 
characteristically brief. The integration is a multiform grey 
flash which is independent of the quality of the stimulus but 
is directly determined by the temporal interval between the 
exposures of the two stimulus-members. The spatial attri- 
bute is a constant factor for any one exposure, but may vary 
from exposure to exposure (as the perception of movement 
also varies between optimal and partial). There is, then, no 
movement in the multiform grey flash ; the space is constant ; 
the integration is of time and quality. 

Wertheimer, finding that there " is no visual filling-in of 
the field of movement," argues that the perception of move- 
ment must have as its physiological correlate a short-circuit 
in the cortex. The grey flash which we have found to be the 
psychological correlate of the perception of movement obvi- 
ates the necessity of such recourse to novel and speculative 
conditions. 

12 D. Katz, Die Erscheinungsweisen der Farben, 1911, 6ff. 

13 H. Sheppard, Foveal Adaption of Color, Amer. Jour. Psy., xxxi 
1920, 58. 



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